Motorized scythes or free-cutting tools of known configuration have a drive motor especially in the form of an internal combustion engine which drives a cutterhead via a shaft supported in a guide tube. The cutterhead is rotatably driven about a rotational axis. The cutterhead carries a cutting filament which rotates in a rotational direction when the cutterhead rotates. The cutting filament aligns itself approximately radially to the rotational axis as a consequence of the developed centrifugal forces. In its rotational direction, the cutting filament defines a cutting circle having a nominal radius which is constructively pregiven. A protective shield is provided in the region of the cutterhead and this shield covers the cutting filament at least partially over its cutting circle.
For cutting different plant matter such as grass or the like, the free-cutting tool is aligned in a usual work position so that the cutting circle lies approximately parallel to the surface to be processed. The rotating cutting filament cuts the plant matter in the plane of the cutting circle.
The cutting filament is made of a flexible plastic and is subjected to wear which causes the cutting filament to become shortened. A cutting circle arises with a radius which is less than the nominal radius pregiven constructively. The cutting capacity of the free-cutting tool is reduced.
A manual or automatic readjustment of the cutting filament is necessary from time to time. For this purpose, the cutting filament is moved out of a magazine from the cutterhead in order to compensate the loss of length caused by wear. The length compensation takes place mostly with an excess. A cut-to-length knife for the cutting filament is mounted on the protective shield at the peripheral region of the cutting circle in order to prevent the formation of a cutting circle having too large a radius, that is, in order to adjust the cutting circle to its nominal radius pregiven constructively. In the first rotational movements following the length compensation, a free end of the excessively long cutting filament impinges upon the cutting edge of the cut-to-length knife and is automatically cut to the length which is not to be exceeded. A nominal radius is thereby imparted to the cutting circle.
A free-cutting tool having a protective shield and an integrated cut-to-length knife is disclosed in U.S. Pat. No. 5,351,403. The cut-to-length knife is mounted at the peripheral end of the cutting circle. Its cutting edge extends perpendicularly to the cutting circle and axially parallel to the rotational axis of the cutterhead. After the automatic cutting to length of the cutting filament by means of the above-mentioned cut-to-length knife, the cutting filament has a free outer end which, in further operation, is cyclically guided past the cutting edge of the cut-to-length knife at high rpm. In this region, an unwanted high level of noise is generated.